Metal Surface Preparation by Plasma-Polymerized Films

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Abstract
Thin films (<1000 Å thickness) were deposited by polymerization in an RF plasma of hexamethyldisiloxane (HMDS) and ethylene on cold-rolled steel (CRS), electrogalvanized steel (EGS) and on polished pure zinc substrates. Prior to deposition the metals were cleaned in a reactive or nonreactive plasma in the same reactor. The films were characterized by various analytical techniques (FTIR, TOF-SIMS, XPS, and AES) for structure, composition, and metal-polymer interfacial composition. All plasma films appeared to be highly polymerized, crosslinked, and virtually insoluble in organic solvents. The ethylene films also showed a high degree of aromaticity and unsaturation. Both types of films afforded excellent resistance of the metal substrate to corrosion in humidity tests at elevated temperatures. The films were stable in air at temperatures up to at least 175°C. Some films provided corrosion resistance even after severe deformation by deep drawing a 5 cm diameter dome in the panel. The corrosion resistance of the film deposited on zinc substrates was usually better than that of the same films on CRS. Analysis by AES indicated that the film-metal interface compositions for these two metals were different. These differences will be related to the surfaces of the substrates.